Nonaqueous secondary batteries with a high energy density, such as lithium ion secondary batteries, are widely used for power sources of notebook computers, mobile phones, etc. Further, in addition to power sources of power tools and power sources of electric cars, the development of nonaqueous secondary batteries as, for example, power sources of portable electronic devices, such as mobile phones and notebook computers, has recently been progressing.
Thus, lithium ion secondary batteries are currently used for various power sources. One reason for this is that the use of lithium ions, which are elements with the highest ionization tendency, as a charge carrier allows a reduction in the potential of the negative electrode; consequently, the voltage as a battery increases. Nonaqueous secondary batteries using sodium ions, magnesium ions, or the like as a charge carrier are also known as post-lithium ion secondary batteries. In principle, however, the potential of the negative electrode is not less than the potential of metal lithium; after all, the performance of many post-lithium ion secondary batteries is much lower than that of lithium ion secondary batteries, which use lithium ions as a charge carrier.
Moreover, dendrite formation is one of the main drawbacks in nonaqueous secondary batteries using metal ions as a charge carrier, such as lithium ion secondary batteries. Various measures are taken to prevent dendrite formation; however, there is no sufficient solution.
On the other hand, an example using a salt containing a molecular ion is also known (e.g., PTL 1). In this case, however, lithium ions were used as a charge carrier bearing a negative electrode reaction.